Tag Archives: wireless

The IEEE 802.11 family of standards, marketed under the Wi-Fi brand, has continued to offer users increasingly higher data rates since the late 1990. Published in December 2013, the 802.11ac amendment brought substantial improvements in data rates over its predecessor, 802.11n. The 802.11ac provides a maximum theoretical data throughput of 6.93 Gb/s using:

Up to 8×8 multi-user multiple-input multiple-output (MU-MIMO)

Larger channel bandwidths of 80 and 160 MHz

Higher order quadrature amplitude modulation (QAM)

Breaking the gigabit barrier

Using channels of up to 160 MHz wide and higher order modulation increase the peak data rate for 802.11ac up to 866.7Mbps, or 333 percent over 802.11n for a single spatial stream (SS). Moreover, a wireless access point (AP) with dual antennas can support a peak data rate of 1.7Gbps. With 8 antennas and 160Mhz channel, the total capacity can reach 6.93Gbps.

Operation in the 5GHz band

Wi-Fi is designed to operate in the unlicensed industrial, scientific and medical (ISM) radio bands around 2.4GHz and 5 GHz. 802.11ac utilizes the 5GHz band from 5.15GHz to 5.875GHz, exclusively. The radio bands available in the 5GHz are a mix of ISM and Unlicensed National Information Infrastructure (U-NII) bands.

The larger available spectrum in the 5 GHz band provides more non-overlapping channels than the 2.4GHz band. In addition to the 20 and 40Mhz modes, IEEE 802.11ac also supports three new expanded channel bandwidth modes: 80, 160 and 80+80Mhz. The 80+80 mode combines two non-contiguous 80Mhz channels into one 160Mhz channel. As in the 2.4GHz band, each country has specific regulations that determine how much of these bands are made available.

Not all the channels in the 5 Ghz band are useable all the time and various restrictions are placed on their use. Certain radar systems are primary users in the 5 GHz band and it is important to ensure that WLAN equipment does not interfere with them. WLANs can coexist with radar systems using dynamic frequency selection (DFS) mechanism that automatically selects a frequency that does not interfere with the radar systems while operating in the 5 GHz band.

Backward compatibility

802.11ac is backward compatible with 802.11a and 802.11n devices operating in the 5GHz band. This means that 802.11ac can communicate with 802.11a and 802.11n clients without issues. 802.11ac, however, does not provide backward compatibility with technologies that uses 2.4Hhz band, such as 802.11b and 802.11g. Therefore, access point (APs) must have dual-band capability to support these clients.

MIMO scheme

In a MIMO (Multi-input Multi-output) scheme, the transmitter divides a data stream among N transmitting antennas. The antennas receive these sub-streams as (multiple) input and broadcast them. The other end receives the transmissions using M antennas. The (multiple) outputs from all the M receiving antennas is combined to get the original data stream. The MIMO scheme improves the reliability and results in a higher link capacity. A single user MIMO (SU-MIMO) allows the AP to communicate with one user at a time.

MIMO schemes are characterized by the number of antennas used, MxN. For instance, a 2×2 MIMO refers to two antennas at the transmitter side and two antennas at the receiver side.

MU-MIMO

802.11ac includes MU-MIMO modes, which allow simultaneous data transmissions to multiple devices using space-division multiplexing (SDM). Up to four clients can receive simultaneous transmission from an AP. Each client may receive up to four SSs without exceeding the total number of eight SSs. MU-MIMO is downstream capability, upstream traffic from client proceed in half-duplex mode after normal avoidance mechanisms are employed.

With SU-MIMO, adding more stations with fewer antennas to an AP increases contention and degrades performance. In contrast, MU-MIMO allows more low-cost devices to connect to an 802.11ac AP without sacrificing throughput.

Power and connectivity requirements

The power requirements of 802.11ac are higher than previous standards due to additional SSs and more sophisticated signal processing. Thus, 802.11ac APs cannot work within the power budget of the standard power-over-Ethernet, 802.3af. Instead, power to 802.11ac APs can be supplied using 802.3at (PoE+) that provides up to 25.5 watts. Alternatively, APs can be powered by DC power adapters if their use is feasible at the APs’ locations.

The higher capacity has an implication also on the connectivity to the wired infrastructure. It is common for 802.11ac APs in the market today to have two 1Gbps ports. Also, multi-gigabit ports (2.5/5.0/10Gbps) are likely needed to support higher-end APs.

Coverage

Higher spectrum band generally means shorter range and smaller coverage area. That is because 5GHz signals attenuate faster than 2.4GHz signals do and they do not penetrate as many obstacles. However, 802.11ac can cover the same nominal range the 5Ghz 802.11n.

Applications

Some of the goals of 802.11ac is to deliver higher levels of performance that enable applications such as:

The mainstream consumer market started seeing Wi-Fi products based on IEEE 802.11ac standard in 2013. The standard is the fifth generation of Wi-Fi networking technology that promises more bandwidth to users at home and the office. The new Wi-Fi brings new improvements to wireless networks including offering 1.3Gbps of bandwidth (in the so-called Wave 1) and the ability for an access point (AP) to communicate with more than one client device simultaneously. The standard operates only in the 5 GHz band instead of 2.4 GHz band, which means better performance and no interference with legacy Wi-Fi devices, cordless phones, and Bluetooth [1].

Until now, wireless local area networks (WLANs) were considered low performing compared to their wired counterparts. Security and reliability concerns also contribute to assigning WLANs a secondary role in organizations to provide limited services, such as guest connectivity to the Internet or temporary connectivity to employees in boardrooms.

As wireless standards such 802.11ac and future standards are raising the bandwidth ceiling to new heights, the WLAN performance will not be a bottleneck any longer. The next upgrade to 802.11ac, Wave 2, increases the theoretical maximum bandwidth to 7Gbps. A new standard, 802.11ad, will offer 7Gbps bandwidth in the 60GHz spectrum band and will be marketed as Wi-Gig [2]. Also, the work on 802.11ax, the Wi-Fi successor of 802.11ac, is already in progress to provide even higher connection speeds [3].

The imminent future of gigabit wireless will enable applications that were only possible with wired networks, such as VoIP, videoconferencing, and streaming media. Moreover, trends such as BYOD and the ubiquity of mobile devices used by employees may motivate employers to replace their wired LAN with WLANs as their primary infrastructure rather than maintaining two distinct LAN technologies. This approach is also attractive economically as wireless infrastructure requires less ports per user, therefore, saving the cost of switches, equipment cabinets, and cabling.

Home users already moving away from wired networks. Laptops, tablets, and game consoles are expected to connect wirelessly, and now service providers are offering wireless TV receivers, severing more ties to the wired LANs [4]. The trend towards smarter homes is bound to increase the demand for wireless home networks as more sensors, security cameras, smart lighting devices and others are accessed and controlled remotely by the user.

The decision to switch to wireless as primary LAN technology is not straight forward. Security concerns, both real and perceived, need to be addressed. There are also significant costs associated with upgrading the backbone wired network to be able to deliver multi-gigabit pipes to each wireless AP in addition to the cost of deploying and managing the wireless infrastructure itself. Nevertheless, some experience deploying wireless as primary LAN technology has showed significant cost benefits [5][6].